The studies proposed in this application are designed to determine the relative importance of vasopressin in the daily regulation of arterial pressure, body fluids and electrolytes. The experiments differ from those being conducted in many other laboratories in that they are designed to obtain quantitative data regarding the role of vasopressin in both the acute and long-term control of these variables. Utilization of a highly sensitive and efficient vasopressin radioimmunoassay will enable the quantification required for these studies. This, in conjunction with development of techniques for continuous and long-term monitoring of hemodynamic variables in unanesthetized dogs, will provide the needed quantitative data. (1) A series of studies is designed to determine the short-term feedback gain, time-response, and range of operation of the vasopressin-pressure control system and the vasopressin osmo-control system. The extent to which factors such as anesthesia, the renin-angiotensin system and the sympathetic nervous system can alter the acute and long-term feedback gain of the system will be studied. (2) The relative short and long-term influence of the major factors controlling vasopressin secretion will be quantitatively evaluated including extracelluar osmolality, low and high pressure baroreceptor receptors, and angiotensin. (3) The ability of vasopressin to exert a long-term influence on arterial pressure by its interaction with the salt-retaining hormones and the sympathetic nervous system will be studied. (4) Normal human subjects will be studied to determine acute and chronic responses of vasopressin to various types of sodium and volume loads. (5) Finally, the quantitative data obtained in these studies will be evaluated by computer modeling techniques.